"Google has revealed that it has no plans to develop dedicated apps for Windows 8 or Windows Phone 8 for its business app products such as Gmail or Drive." Product management director for Google Apps, Clay Bavor, told V3 that Google "will go where the users are but they are not on Windows Phone or Windows 8". Ouch - but for now, hard to argue with.

Microsoft has been less aggressive towards Android in the patent wars. How long we don't know.
I goes to reason that you would rather foster a market for the less aggressive competitor then the others.
Which will undermine sales of the aggressor.
Releasing Windows apps might help in this regard.